Cheapest way of preventing electrolytic corrosion

[cheb]

I've a trailer with a steel frame and an aluminium bed, it's doesn't get much use, lives outside and it's generally covered in salt from the winds up here. I'm rebuilding it and while it's apart I'd like to try to slow the corrosion.

I was thinking about using dpm, possibly stuck on with silicone or similar.

Any suggestions?

 

[grim_d]

I'd think just isolating it with a fay seal using appropriate sealant would be enough?

Unless you want it removable in which case the dpm is a decent idea

 

[colnerov]

A good coat of paint will work as well.

 

[8ob]

A good coat of paint will work as well.

Or drown the whole underside in Waxoil.

Bob

 

[grim_d]

Or drown the whole underside in Waxoil.

Bob

Ah waxoyl....modern stuff does more damage than good, every time I see the underside of a vehicle that's been done with it it's just a horrific crusty mess, a thick layer of flakey black rubbish that continually traps moisture and salt in a never ending cycle. Terrible stuff.

4 years ago I did mine with dynax clear (others are available!) And it's 95% as good as the day I did it, just one or two edges on things like the subframe that I obviously didn't catch quite right.

 

[cheb]

I'm considering having the fame galvanised once I've drilled all the holes etc when rebuilding it. The biggest challenge on costs is the logistics of getting it to and from the galvanisers. Probably easiest to tow it and dismantle it in their yard, if they'll let me.

 

[Rrobson]

Are you suffering with excessive corrosion? Steel and aluminium are quite well matched and is the reason cars can have aluminium engines without too many problems.
Otherwise any barrier will do but make sure you completely insulate the fasteners too otherwise it defeats the object…

 

[hermetic]

Aston Martin used to use strips off cotton cloth impregnated in waxoyl or similar folded round the edges of the steel tub befpre the aluminium body skin was clenched onto it. seemed to work well. You must try to completely eliminate the ingress of moisture into the joint. bitumen felt and waxoil might do it. Pay special attention to the through bolt fixings and use felt washers. Ideally you need the dissimilar metals to be electrically seperated. not easy!

 

[hermetic]

That black crap is not the waxoil I am talking about! I mean silicon wax suspended in white spirit base which soaks into the rust and seals out the air. THE original Waxoyl (tm) Morrises do one called Ankorwax, same stuff

 

[voipio]

Might the issue be salt water corrosion, rather than galvanic, as such?

The introduction in the paper linked to below is interesting, in this regard:

https://www.osti.gov/etdeweb/servlets/purl/20671863

I remember crossing the Kyle of Durness, en route to Cape Wrath, in a boat whose hull was made from aluminium panels welded together.

 

[OJCar]

DPM between the alloy and the steel is nice and cheap.
There is Duralac sealer you can use as well, usefull where the steel bolts pass thro the alloy.
https://www.mbfg.co.uk/duralac.html

 

[cheb]

I was planning using gravity to keep the bed in place, helped by the sides pressing down.

I've a vague memory of their being a problem with oily woods, teak and the like, being in close contact with galvanising. Anyone confirm or deny before I end up down the search engine rabbit hole with equally definitive and vehement arguments on both sides.

 

[Spark plug]

What about using some of that structural adhesive that they glue car bodies together with these days. Will eliminate the need for fasteners and create a barrier between the two materials.

 

[Hood]

Aluminium, steel and salt water is the worst combination you can have, Isolating with something will help but just make sure any bolts are isolated from the aluminium as well.
Often on boats where steel and aluminium fix together we put rubber in between and make flanged washers from Delrin to keep any steel fixings away from the aluminium.